The need to know one's location arises in many situations. For example, an operator of an aircraft, spacecraft, ground vehicle, or the like needs to know the location of the craft or vehicle in order to properly maneuver the vehicle and avoid dangerous conditions. In addition, unmanned vehicles, such as unmanned aerial vehicles (UAVs) or mobile robots also need accurate position and velocity information in order to properly navigate an area.
On and around Earth, precise navigation can usually be resolved with the aid of a Global Positioning System (GPS) sensor. However, GPS signals are not always available. For example, a GPS signal may not be available when a vehicle is traveling in a city among tall buildings or through large canyons. When GPS signals are not available, precision navigation becomes more difficult. In the absence of GPS signals, most current known navigation methods are susceptible to drift.
Technologies related to navigation in the absence of GPS signals are receiving much attention both from the military and commercial sectors. Typical approaches only provide for relative navigation, which means that the only way a platform can navigate is by dead reckoning. Dead reckoning is the process of estimating one's current position based upon a previously determined position, and advancing that position based upon known speed, elapsed time, and course.
Modern inertial navigation systems, which depend upon dead reckoning, are widely used in various manned or autonomous vehicles. Such inertial navigation systems use a computer and motion sensors to continuously track the position, orientation, and velocity of a vehicle without the need for external references such as a GPS. The main component of such inertial navigation systems is an inertial measurement unit (IMU). An IMU works by sensing its own rate and direction of motion using a combination of accelerometers and gyroscopes, which then allow a guidance computer to track vehicle position using dead reckoning.
A serious problem with dead reckoning is integration drift. As dead reckoning uses an integration method to navigate, velocity/rate estimate errors are integrated, leading to a random unbounded drift of the navigation position/attitude solution. Thus, there is a need for techniques that can be used to limit the effects of integration drift by minimizing the errors in the velocity/rate estimate.